Idea: Improve Github wiki.

[rvid19]

Hi, I started playing Freeciv last year and it's a very good game, but it's just that it's hard to find how to play. So an idea I had is to improve the GitHub wiki, for example:

• Add a unit catalog with how to use each unit.
• Document what all server options do, as they are many for new players.
• List tile improvements, buildings, and wonders and what they do.
• Add welcoming message to new repo contributors.
• List all music songs.

These are just suggestions, but let me know what you think. :)

[cazfi]

freeciv/freeciv-web uses rulesets of the freeciv.org desktop freeciv, so, e.g., manual on https://www.freeciv.org/wiki/Rulesets/3.1/civ2civ3 is quite close.

[rvid19]

@cazfi I edited the GitHub wiki. Do you have any feedback? :)